Angle of arrival (AOA) measurement is a method for determining the direction of propagation of a radio-frequency wave incident on an antenna. AOA determines the direction by measuring the Time Difference of Arrival (TDOA) at individual elements of an antenna array; the AOA can be calculated from these delays.
Generally, this TDOA measurement is made by measuring the difference in received phase at each element in the antenna array. This can be thought of as beamforming in reverse. In beamforming, the signal from each element is delayed by some weight to “steer” the gain of the antenna array. In AOA, the delay of arrival at each element, which corresponds to the phase of the incident wave, is measured directly and converted to an AOA measurement.
Because AOA measures the difference between two or more received phases, AOA generally relies on multiple antennas coupled in an antenna array.